>All this brings up the basic point:
>
> What is the definition of an answer?
>
>I don't think that this question has been satisfactorily answered.
Indeed, and that may be the basic problem we are having here. Your
idea of answer apparently differs from Ian's, for example.
My own view on this is that there is no *definition* of an answer,
but there are some conditions that all answers must satisfy. The only
condition that everyone will likely agree on is that any answer must
be entailed by the KB. (That is, that the instance of the query with
that binding is entailed by the KB.) I think in fact that this is
*all* that should be required in a spec., and that any attempt to
ensure that 'all' answers are given, or that logically equivalent KBs
must give identical answers, are misguided in the SW context; they
are far too strong to permit implementors to experiment, so will in
fact simply be ignored in practice; and in any case I do not think
that they are sensible in a Web open architecture. So I'm afraid that
I find this debate somewhat pointless and timewasting.
Assuming that we do want to define something like the 'answer set' (I
would like to see some rational explanation for why this concept is
useful, by the way) , Ian has argued strongly that it should not
include all 'answers' that can be logically inferred from the KB, but
only those which arise from a binding of a query variable to a term
in the KB Herbrand universe, in order to keep the inferential burden
on the server within DL-manageable bounds. I am happy with that; but
given the resulting incompleteness, it seems silly to object to a
proposal on the grounds that logically equivalent KBs may not always
deliver the same answers.
The point of the MID construction was to provide some useful
information to the querying system in the case where a binding itself
provides no useful information. We can debate the technical details
of how best to do this, but that some such mechanism is needed seems
to me to be obvious. In particular, any proposal for defining
'answer' which arbitrarily forbids a server from transmitting useful
information to a querying engine, when it has already had to compute
that information in order to answer the query, seems to me to be so
mind-blowingly stupid as to not be worth discussing further.
Pat
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